The present invention relates to a yarn false twist texturing apparatus or machine of the general type disclosed in DE 31 21 959.
Texturing is intended to impart to a substantially flat yarn a more textilelike appearance and the therewith connected characteristics. To this end, the flat yarn being fed to the texturing machine is twisted in the texturing machine by a twisting unit. Subsequently, this false twist is set in the yarn within a false twist texturing zone by heating the twisted yarn in a heating device. Subsequent to the heat treatment, the yarn must again be cooled by a cooling device. To this end, the yarn spirals in the known texturing machine around the outer surface of a cooling tube, which is cooled in its interior by a coolant. The spiral advance of the yarn achieves on the one hand a stable yarn path in the texturing zone and on the other hand an improved heat transfer between the yarn and the cooling device.
In texturing machines of this kind, it is currently common practice to use heating devices, which exhibit a heating temperature that is above the melt point of the yarn material. These so-called high-temperature heaters make it possible to keep the texturing zone relatively short despite the high yarn speeds of up to 1,200 m/min. Thus, besides the intensive heating of the yarn, it is necessary that an intensive cooling adapted to the heating of the yarn be effected in the cooling device.
In the texturing machine known from EP 0 744 481, it is proposed to subdivide the cooling device into two zones. In a first zone, a plurality of openings are arranged in the jacket of a cooling tube. It is thereby realized that the yarn advancing on the outer circumference of the cooling tube comes into direct contact with a coolant. However, this arrangement has the disadvantage that it causes an increased portion of volatile components to separate from the yarn, which can be taken in and removed only by an additional suction device. Furthermore, such a direct contact of the yarn with the coolant on the cooling tube leads to an unstable yarn advance even in the second zone, in which the yarn advances on the outer surface of the cooling tube.
It is therefore an object of the invention to further develop a texturing machine of the initially described type wherein a yarn can be intensively cooled as rapidly possible, even at high yarn speeds and a high temperature load in the heating device.
A further object of the invention is to provide a texturing machine with a cooling device, wherein a plurality of parallel arranged cooling tubes can be supplied in a simple manner by one source of coolant.
The above and other objects and advantages of the invention are achieved by the provision of a yarn false twist texturing apparatus which comprises a yarn heater, a yarn cooling device, and a yarn twisting unit serially arranged along a yarn path of travel. The yarn cooling device comprises a cooling tube which defines an upstream end adjacent the yarn heater and an opposite takeoff end, and the cooling tube is sized and positioned for having the advancing yarn spirally advance thereover from the upstream end to the takeoff end. A source of cooling fluid is arranged to flow through the interior of the cooling tube in a direction from the takeoff end to the upstream end so as to cool the cooling tube from the inside and cool the yarn as it advances along the cooling tube.
The special feature of the invention lies in that the cooling effect of the cooling tube is intensified toward the takeoff end. This prevents the yarn from undergoing a shocklike cooling, as it contacts the cooling tube. Since the coolant flowing from the takeoff end to the upstream end is already heated by the constant heat transfer between the outer surface and the coolant, the upstream end of the cooling tube is less cooled by the coolant than the takeoff end of the cooling tube. A further advantage lies in that upon leaving the cooling device, the yarn has a uniform temperature, since the outer surface of the cooling tube has in the takeoff end a temperature that is determined by the coolant supplied thereto. The coolant flowing opposite to the direction of the advancing yarn provides that the yarn guided on the outer surface contacts a surface, which becomes constantly cooler, and thus undergoes a more effective cooling, which has an especially favorable effect on the setting of the crimp in the yarn.
In the preferred embodiment, the takeoff end of the cooling tube is closed, and the yarn cooling device further includes an inner tube positioned coaxially within the cooling tube so as to define a passage which extends axially between the inner tube and the cooling tube. The inner tube has a discharge end adjacent the closed takeoff end of the cooling tube and an opposite inlet end adjacent the upstream end of the cooling tube, and the discharge end of the inner tube has at least one opening therein. The inlet end of the inner tube is connected to the source of cooling fluid, so that the cooling fluid flows through the inner tube and exits into the passage through the opening in the discharge end and then flows back through the passage toward the upstream end of the cooling tube. In this process, the outer surface of the cooling tube is cooled.
The upstream end of the cooling tube preferably forms an outlet which communicates with the passage and through which the coolant exhausts. With this configuration, all connections may be arranged at one end of the cooling device, i.e. the cooling device connects to the source of the coolant only at one end. The opposite end of the cooling device has no connections whatsoever, so that the length of the texturing zone is essentially dependent on the operative lengths of the heater and the cooling device.
The cooling passage extends along substantially the entire length and circumference of the outer cooling tube, which provides uniform cooling on the outer surface of the cooling tube.
It is also preferred that the inner tube have a free flow cross section, which is greater than that of the cooling passage. This results in the heat being quickly removed from the cooling tube, and the outer surface undergoes in addition an intensive cooling.
Preferably, the free flow cross section of the inner tube is made at least twice as large as the free flow cross section of the cooling passage.
In a particularly preferred embodiment of the texturing machine, the coolant used is a cooling air. In this instance, the source of coolant includes a blower. Since the coolant has a temperature ranging from 10xc2x0 to 40xc2x0 C., it is preferred in such case to make direct use of the ambient air as the coolant. The cooling device distinguishes itself in this case by its simple and yet effective construction.
In cases where the texturing machine is operated in a surrounding with higher air temperatures, it is desirable to construct the texturing machine to include an air-conditioning system which is directly used as the source of coolant and is connected to the cooling device.
With the use of a cooling air, it is preferred to arrange the cooling device of the texturing machine in an open coolant circuit. To this end, the texturing machine of the present invention is designed and constructed so that the heated cooling air is released directly to the surroundings via the outlet opening of the cooling tube.
To change the contact length and, thus, the intensity of the heat transfer between the yarn and the outer surface of the cooling tube, it is preferred to provide each cooling tube of the texturing machine of the present invention with an inlet yarn guide and an outlet yarn guide. By adjusting the inlet yarn guide or the outlet yarn guide in a circumferential direction, it is possible increase or decrease the looping about the cooling tube. To intensify of the cooling, the looping of the yarn about the cooling tube is increased. With that, the contact pressure of the yarn is increased, so that a more intensive cooling of the yarn occurs. This further development makes it thus possible to realize a fine adjustment of the yarn temperature at the takeoff end.
To obtain a uniformly satisfactory crimp quality, the cooling device extends with the yarn heater and the first feed system in a common plane upstream of the twisting unit. This prevents the yarn from undergoing in the twist zone an additional deflection, which impedes a return of the false twist in the yarn to the heater.
With the use of a plurality of parallel side by side cooling devices, it is possible to supply at the same time a plurality of cooling devices arranged side by side by one source of coolant. To this end, a collection tank or manifold is arranged between each cooling device and the source of coolant. From the manifold, the coolant reaches under the same pressure the cooling devices connected to the manifold. This system is therefore especially preferred for use in an open coolant circuit.